The present invention relates to safety features in downhole tools and in particular to a safety trip button to prevent premature setting in weight set downhole tools.
A number of downhole tools as used in the oil and gas industry are operated within a well bore by contacting or landing part of the tool onto a formation located within the well bore. Typically a sleeve of the tool is landed on a liner top PBR (polished bore receptacle), causing the weight of the tool to force the tool into the liner while the sleeve remains stationary on the liner top. The relative movement of the sleeve on the tool body operates the tool, for example by opening radial ports or by compressing a packer.
In order that the sleeve does not move when the tool is inserted or run into the well bore, shear pins are typically inserted between the tool body and the sleeve to hold the sleeve in place. When the tool is landed on the liner top, the relative movement of the sleeve to the tool body causes the pins to shear thereby allowing operation of the tool.
A major disadvantage of these weight set tools is that they can be operated by the sleeve contacting any formation in the well bore. For example if the sleeve comes into contact with debris adhering to the walls of the casing or at a casing joint where the internal casing diameters are mismatched, the sleeve may be jarred or stick at that point in the well bore. Once stationary the tool body may be free to fall with a sufficient relative force to shear the pins. Thus the tool will be activated and operate at the incorrect position in the well bore.
It is an object of at least one embodiment of the present invention to provide a safety mechanism to prevent premature setting of a weight set tool in a well bore.
It is a further object of at least one embodiment of the present invention to provide a safety trip button which shears only when a weight set tool contacts a selected formation in a well bore.
It is a yet further object of at least one embodiment of the present invention to provide a compression set packer tool which includes a safety mechanism to prevent premature setting of the packer.